1. Field of the Invention
This invention relates in general to machines, and a sewing station therefore and in particular to a new and useful device for controlling the positioning of a workpiece in a sewing machine.
U.S. Pat. No. 4,555,998 discloses a feed device with a steering mechanism which holds a holder for the product being stitched and that is guided in two coordinate directions. The steering mechanism is driven by stationary stepping motors that execute an appropriate number of drive steps overlapping in time to move the product being stitched in the desired manner. The stepping motors can be controlled by a microcomputer that calculates the necessary number of drive pulses from position data that are taken from a memory.
When the control and the stepping motors operate routinely, the feed device operates satisfactorily. However, when there are disturbances in the control or drive areas, there is a risk that the holder for the product being stitched will execute a motion other than the predetermined motion, for example when data are lost from the memory by polling or by transmission to the stepping motors. The needle can then strike outside of the recesses provided on the holder for the product being stitched, and can be damaged or destroyed. The invention provides a construction for a sewing machine capable of preventing damage or destruction of components of the stitching area of a sewing station having a feed device when its holder for the product being stitched executes a motion differing from a predetermined motion.
There is a motion relationship determined by the transmission mechanism between any arbitrarily selected point on the holder of the product being stitched and one of the parts movable relative to the sewing machine provided to drive or guide the holder from the product being stitched. For this reason, the motion of the holder for the product being stitched can be monitored at any arbitrary mechanically suitable and advantageously readily accessible point on these parts if the motion relationship is known.
The sensor used can operate optoelectronically, electromagnetically, pneumatically, or mechanically, and has a transmitter and a receiver, or in the case of mechanical design, a sensor pin and a limit switch. The marking, for example, is designed as a device to be monitored, as a line drawn on a plate or as a scanning slit provided in the plate, and is designed so that it conforms to a stitching slit incorporated in the holder for the product being stitched with consideration of the motion relationships of the feed device based on the transmission mechanism.
The sensor device and the marking execute a motion relative to one another in which one of the two devices is held on at least one of the movable parts of the feed device, while the other device is in a stationary position in its range of motion. Because of this measure, a deviation from a predetermined motion is detected immediately by the sensor.
The switching signal triggered by the monitor can produce a correction of the error in dependence on the design of the control circuit controlling the drive mechanism, for example, so that the holder for the product being stitched is moved along with the predetermined course of motion. Another possibility is to turn off the drive mechanism through the control circuit until the error is eliminated.
In one embodiment the sewing station has an optoelectronic sensor device, since the receiver of such a system reacts extraordinarily rapidly and sensitively to a very slight change of the amount of light. In addition, the scanning head can be placed at a favorable, readily accessible location at some distance from the marking, without its accuracy of measurement being significantly affected thereby.
Another embodiment makes it possible, after a change of the form of stitching, to interchange the plate having a different marking with the previously used plate in the shortest possible changeover time by seating it on the carrier.
In one embodiment the sensed signal turns off the drive and prevents damage to components of the stitching area of the sewing station by relatively simple means of control.
Accordingly, it is an object of the invention to provide a device for controlling the positioning of a workpiece in a sewing machine which has a drive for a needle which reciprocates at a sewing station in order to sew the workpiece, and which comprises a holder engageable with the workpiece for advancing it through the sewing station in a selected path; and which includes a feed device driven by the drive and connected to the holder for moving the holder with the workpiece, and which also has a monitoring means associated with the holder for monitoring the position of the holder with the workpiece and connected to the feeding device for controlling the movement of the holder.
An object of the invention is to provide a sewing station for a sewing machine which has a feed device which comprises a holder for the workpiece being stitched that is driven by the feed device or drive mechanism to execute a predeterminable motion, which also includes a monitor moveable as a function of the motion of the holder which has markings corresponding to a predetermined motion and which includes a sensor which scans the markings and a control circuit which is connected to the sensor and the feed device which emits switching signals to the feed device when the holder for the product being stitched deviates from the predetermined motion.
A further object of the invention is to provide a scanning control device for the operation of a sewing machine feeding mechanism, which includes a holding plate for guiding the workpiece having a stitch slit opening to which the needle is moveable to sew the workpieces, and which includes means for scanning movement of the holder so as to regulate the feed of the holder through the operation of two separate stepping motors which acts to drive the feed mechanism to position the holder.
A further object of the invention is to provide a device for controlling the positioning of a workpiece in respect to a reciprocating needle, which is simple in design, rugged in construction and economical to manufacture.